This invention relates to a method of producing a crusher wear part and the like subject to gouging abrasion type metal loss and, more particularly, to providing a crusher wear part or the like having a substantially greater wear life than the heretofore used Hadfields manganese steels.
I have determined that it is important for the maximization of wear resistance to balance the carbon and aluminum alloying ingredients in the manganese steel.
A principal deterrent for utilizing aluminum is that its presence in manganese steel can cause considerable problems when the manganese steel is used as scrap in producing other manganese steels. Aluminum is difficult to remove and is an undesirable ingredient of most manganese steels. But on the other hand, it is distinctly advantageous to reprocess the worn crusher parts. Foregoing this reclamation is tolerable if the parts provide a longer wear life--thus justifying the loss of the scrap value.
Aluminum is known as an alloying ingredient in manganese steels but for entirely different purposes and in differing amounts and relationships to carbon than is provided here.
This invention is based on the discovery that the relationship of aluminum to carbon must be carefully regulated in a manganese steel to achieve a wear resistance higher than that of conventional Hadfields steel. More particularly, the aluminum to carbon ratio must be in the range of 1.0 to 1.7 to develop the advantages of the invention. The ranges of alloying ingredients are as follows:
______________________________________ Carbon 1.4-1.8 Manganese 12-20 Silicon 0-1.0 Chromium 0-2.5 Nickel 0-3 Molybdenum 0-2 Vanadium 0-1 Aluminum 1.5-2.5 Iron remainder ______________________________________
Below an Al/C ratio of 1.0, the castings have excessive carbide film in the grain boundaries and can crack prematurely in use while above 1.7 there is no wear advantage to be gained over conventional manganese steels, so the bother with aluminum is not justified.
The prior art has not appreciated the criticality of the Al/C ration, notwithstanding the wealth of art on aluminum-containing steels. The prior art that appears to be closest to the chemistry of the instant invention are U.S. Pat. No. 4,425,169 and Russian Inventor's Certificate 648,647.
The '169 patent was concerned with developing austenitic manganese steel having an as cast perlitic microstructure with several examples of alloys. There is no indication of the criticality of the Al/C ratio and in fact a contra-indication in that one of the preferred modes has a ratio of 0.82. Equally important is the failure of the '169 patent to teach anything about the use of manganese castings as crusher parts and the resistance thereof to gouging type abrasion.
The '647 Certificate also contra-indicates the present invention. Two of the three examples have Al/C ratios well above 2. Further, the sand abrasion tests referred to would not suggest crusher usage. By and large, manganese steel is a totally unacceptable material for low stress wear applications as contemplated in the '647 Certificate.
More particularly, these references fail to suggest the important of testing the melted constituents for the Al/C ratio and, where necessary, adjusting the amounts of constituents to maintain the al/C ratio within the range of 1.0-1.7.